The present invention relates to printed circuit board (PCB) package technology and more particularly to a method and apparatus for removing heat from a PCB.
Mezzanine cards allow for a variety of optional functional expansions for a host computer system, such as network interfacing, modem communications and security co-processing. Mezzanine cards may even contain a main processor for the host system. Typically, a mezzanine card is connected to a carrier board of the host system using the Peripheral Component Interconnect (PCI) bus for electrical interconnections. Because mezzanine cards typically mount horizontally to the carrier board, they may require less space than traditional PCI expansion cards that mount vertically, at a right angle to a motherboard. Thus, mezzanine cards may be used in applications requiring relatively small enclosures, such as set top boxes and internet appliances.
FIG. 1 illustrates an exemplary embodiment of a mezzanine system according to the prior art, comprising a mezzanine card 100 mounted on a carrier board 104 by standoffs 106. The mezzanine card 100 may comprise a printed circuit board (PCB) 110 having electronic components 112 mounted on a bottom surface of the mezzanine card 100. PCI bus connections may be made with connectors 114, which may mount with corresponding connectors (not shown) on the carrier board. The carrier board may be mounted in an enclosure 120 which may have a faceplate 122 with an opening 124 to receive a bezel 116 of the mezzanine card 100. A connector 118 may be attached to the bezel 116 to provide an interface to the mezzanine card 100, such as an Ethernet network connection.
Typically, the majority of electronic components of a mezzanine card are mounted on the bottom surface of the PCB. Because the electronic components may generate a substantial amount of heat, a heat dissipating device, such as a bottom heat spreader 130, may be mounted on the bottom surface of the PCB 110 to transfer heat from the electronic components which may then be dissipated into the air. However, the surface area of the bottom heat spreader 130 may not be sufficient to adequately cool the mezzanine card 100. Therefore, one of the challenges facing designers is to provide a thermal solution with an increased dissipative surface area. However, physical dimensions of the mezzanine card 100 may be defined by a standard that specifies a volumetric envelope through which no components may protrude. Therefore, another challenge facing designers is to ensure the thermal solution fits within a standard volumetric envelope.